Knee arthroplasty prosthesis and method

ABSTRACT

A knee arthroplasty prosthesis includes a femoral component having multiple pieces with engagement means provided for engaging various pieces of the femoral component to one another following their insertion in the incised area of the femur. A tibial component includes multiple pieces designed for assembly following positioning in the incision. The tibial component includes a Morse taper cavity on one piece of the tibial component and a Morse taper extension on another member of the component for receipt therein.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is based upon and claims priority under U.S.Provisional Application Serial No. 60/358,174 filed Feb. 20, 2002.

BACKGROUND OF THE INVENTION

[0002] In performing knee arthroplasty with conventional kneeprostheses, it has been necessary to form large incisions in order toaccommodate the preparation of the femur to receive the prosthesis andto accommodate the reception of a fairly large prosthesis into theincised femur for implantation on the prepared distal end of the femur.As is appreciated by those skilled in the art, it is desirable tominimize the size of any incision as the smaller the incision, the morerapidly the patient may recover. Prior art prostheses formed with asingle piece metal component having both left and right condylarportions integral with the patellar flange area require large incisionsin order to accommodate implantation in the prepared femur. In contrast,under the present invention, through the use of multiple pieces for thefemoral component, it is possible to greatly reduce the size of any suchincision, thereby reducing the amount of damage to soft tissue from anysuch arthroplasty and speeding the time of recovery. Similarly, it isdesirable to minimize the size of any incision in the tibia during anyimplantation of the tibial component.

SUMMARY OF THE INVENTION

[0003] The present invention is directed to a prosthesis for use in kneearthroplasty including total knee arthroplasty which is minimallyinvasive to the patient and to a method for performing surgery usingsuch prosthesis including the femoral and tibial components thereof.Under the invention, the femoral component and, preferably, the tibialcomponent are manufactured in at least two and possibly three or morepieces. However, it is possible that the tibial component could be asingle piece, monoblock construction as well as modular multipiececonstruction. In both the single piece and multipiece construction,there is also provided a plastic articular surface insert piece. Thepieces are designed to be assembled together following insertion intothe knee. This allows total knee arthroplasty to be performed throughvery small incisions, as small as three inches, in each of the distalend of the femur and proximal end of the tibia. Following insertion, thepieces of the femoral component implanted at the distal end of the femurare joined together with a locking mechanism to form the modular femoralcomponent and the pieces of the tibial component implanted at theproximal end of the tibia are assembled to form the modular tibialcomponent.

[0004] Femoral Component

[0005] The femoral component may have three component pieces for acruciate retaining design and two component pieces for a cruciatesacrificing design. It may be manufactured as two or three separatepieces or manufactured as a single unitary member which is subsequentlycut or otherwise divided into two or three separate pieces. The piecesare provided with a locking joint for retaining the pieces togetherfollowing insertion in distal end of the femur. The locking joint forthe pieces is placed at the area of low patella/femoral contact, a lowstress area of the femur. This corresponds to the anterior chamfer cutof a routine total knee arthroplasty and the area can be easilyreinforced to accommodate the additional thickness of the locking joint.Various locking mechanisms may be employed for joining the piecestogether including screws or a transverse locking pin which may beinserted from the medial side and/or lateral side. The lockingmechanisms of whatever type lock the component pieces together into asolid assembled prosthesis. The prosthesis will be additionallyreinforced by the underlying bone and/or cement fixation and willproduce a durable construction. The patellar flange and the area of anyjoint between assembled components which may be contacted by the patellashould be smoothed and, possibly, recessed to prevent premature wear ofthe patellar member as it tracks over the joint in the femoralcomponent.

[0006] Tibial Component

[0007] The tibial component preferably has two pieces, namely, a tibialbase and a tibial stem. It is also inserted in pieces from the side. Itmay also be a monoblock, one-piece tibial component with pegged or shortstem fixation. The tibial base may have of a flat baseplate withanterior and posterior dovetails and may have a tapered transverse keel.The other piece of the tibial component is a modular stem which isinserted from the top after the baseplate is inserted. This designallows the components to be inserted through the minimal incision andstill have long term stability. The stem is preferably fixed with areverse Morse taper so that it can be driven through the baseplate likea spike.

[0008] Patellar Component

[0009] A standard conforming dome configuration patellar component isutilized, with the main difference being its method of insertion. It maybe inserted without everting the patella. This is accomplished with theuse of special instrumentation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a perspective view of one embodiment of femoralcomponent showing the medial condyle as a separate piece from theremainder of the femoral component.

[0011]FIG. 2 is a perspective view of a second embodiment of femoralcomponent showing the lateral condyle as a separate piece from theremainder of the femoral component.

[0012]FIG. 2A is a sectional view showing a patellar member engaged tothe articulating surface of the patellar femoral flange piece.

[0013]FIG. 3 is a perspective view of another embodiment of femoralcomponent showing both the medial condyle and the lateral condyle asseparate pieces from the patellar femoral flange piece of the femoralcomponent.

[0014]FIG. 4 is a perspective view showing the patellar femoral flangepiece of FIG. 3 taken from a different angle.

[0015]FIG. 5 is a perspective view of an embodiment of femoral componentshowing the patellar femoral flange piece as a separate piece from theremainder of the femoral component.

[0016]FIG. 6 is a front view of the embodiment of the femoral componentof FIG. 5.

[0017]FIG. 7 is a side view of the embodiment of the femoral componentof FIG. 5.

[0018]FIG. 8 is a sectional view taken through line 8-8 of FIG. 6.

[0019]FIG. 9 is a sectional view taken through line 9-9 of FIG. 6.

[0020]FIGS. 10 and 11 are perspective views of other embodiments of thefemoral component showing the patellar femoral flange piece as aseparate piece from the remainder of the femoral component.

[0021]FIG. 11A is a view similar to FIG. 9 for the embodiment of FIG.11.

[0022]FIG. 11B is a sectional view through line 11B-11B of FIG. 11 A.

[0023]FIG. 12 is a perspective view of another embodiment of femoralcomponent showing the patellar femoral flange piece as a separate piecefrom the remainder of the femoral component and showing one form ofdesign for connecting the patellar femoral flange piece to the remainderof the femoral component.

[0024]FIG. 13 is an enlarged view of the circled portion of FIG. 12.

[0025]FIG. 14 is a perspective view of an embodiment of femoralcomponent showing the lateral condyle as a separate piece from theremainder of the femoral component.

[0026]FIG. 15 is an enlarged view of the circled portion of FIG. 14.

[0027]FIG. 16 is a perspective view of another embodiment of femoralcomponent showing the patellar femoral flange piece as a separate piecefrom the remainder of the femoral component.

[0028]FIG. 17 is an enlarged view of the circled portion of FIG. 16.

[0029]FIG. 18 is a perspective view of the tibial component showing thestem portion thereof as a separate piece from the base.

[0030]FIG. 18A is a view similar to FIG. 18 with the added feature of astem extension as part of the tibial component.

[0031]FIG. 19 is a sectional view of another embodiment of tibialcomponent showing the stem portion thereof as a separate piece from thebase.

[0032]FIG. 20 is a perspective view of another embodiment of tibialcomponent showing the stem portion thereof as a separate piece from thebase.

[0033]FIG. 21 is a side view of the tibial component of FIG. 20 showingits implantation in the proximal end of a prepared tibia.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0034] Referring to FIG. 1, there is shown one embodiment of femoralcomponent generally designated by the numeral 10. The femoral componentincludes a first piece 12 having a patellar flange portion 14 and anintegral, unitary lateral condyle portion 16 extending therefrom. Aprior art femoral component would also have an integral, unitary medialcondyle on the opposite side from the lateral condyle portion 16. Underthe present invention, there is provided, as a separate piece, a medialcondyle piece 18 intended to be assembled to the first piece 12following implantation of both the first piece 12 and the medial condylepiece 18 in the patient. The assembly mechanism or locking joint forsecuring the medial condyle piece 18 to the first piece 12 will behereinafter described.

[0035] As shown in FIG. 1, the medial condyle piece 18 is provided witha recess 15 for receiving bone cement and a pair of fixation pins 17.The first piece 12 may also be provided with one or more recesses andfixation pins. If it is desired to have a prosthesis for implantationwithout bone cement, the recesses such as the recess 15 can be replacedby one of several types of porous surfaces well known in the art forbone in-growth.

[0036] Referring to FIG. 2, there is shown a second embodiment of afemoral component 20 having a first piece 22 with a patellar femoralflange portion 24 and an integral, unitary medial condyle portion 26.The second component of this embodiment is a lateral condyle piece 28which may be joined with the first piece 22 following implantation ofboth the first piece 22 and the lateral condyle piece 28 in the femur ofthe patient.

[0037]FIG. 2A shows a sectional view of patellar member P in contactwith the articulating surface of the patellar femoral flange portion 24.

[0038]FIG. 3 shows yet another embodiment of a three-piece femoralcomponent 30. Under this embodiment, there is provided a patellarfemoral flange piece 32, a second piece 34 which is a medial condylepiece and a third piece 36 which is a lateral condyle piece assuming, ofcourse, implantation in the right knee of a patient. If the femoralcomponent 30 were implanted in the left knee of a patient, the secondpiece 34 would be the lateral condyle piece and the third piece 36 wouldbe the medial condyle piece. Each of the second piece 34 and the thirdpiece 36 are joined to the patellar femoral flange piece 32 followinginsertion in the patient's femur by use of a locking joint to behereinafter described.

[0039] All three of the pieces of the femoral component may be providedwith fixation pins 37 and recesses 35 if intended for use with bonecement or a porous surface if intended for non-cemented implantation.

[0040]FIG. 4 is a perspective view of the patellar femoral flange pieceof FIG. 3 taken from a different angle.

[0041] The femoral components 10, 20 and 30 of FIGS. 1 through 3 couldbe used for implantation in either knee. The foregoing description foreach of the femoral components 10, 20 and 30 is based on the assumptionof implantation in the right knee. If they were used for implantation inthe left knee, the pieces identified by the numerals 18 and 34 would belateral condyle pieces, the pieces identified by the numerals 28 and 36would be medial condyle pieces, the portion identified by the numeral 16would be a medial condyle portion and the portion identified by thenumeral 26 would be a lateral condyle portion.

[0042] Referring to FIGS. 5, 6, 7, 8 and 9, there is shown an embodimentof femoral component 40 having two pieces, namely, a patellar femoralflange piece 41 and a condylar piece 42. The patellar femoral flangepiece 41 has a patellar engaging surface 43 shaped to allow anatomicaltracking of a natural or prosthetic patella P. As shown in FIG. 5, thepatellar femoral flange piece 41 has a superior bone engaging surface 46and a patellar engaging surface 43 defining a portion of an inferiorarticulating surface. The patellar femoral flange piece 41 extends froman inferior end 45 to a leading end 48 which is contoured to engage thecondylar piece 42. The condylar piece 42 includes a first condylarportion 50 and a second condylar portion 52 and extends from anengagement end 54 contoured to receive the leading end 48 of thepatellar flange 41 to a posterior end 55. As will be appreciated bythose skilled in the art, the femoral component 40 could be used forimplantation in either a right knee or left knee and the first andsecond condylar portions will be either lateral or medial facingdepending upon the knee in which the femoral component 40 is implanted.

[0043] The condylar piece 42 has a superior bone engaging surface with aseries of bone engaging flats 60, 61, 62 and 63 disposed at varyingangles consistent with cuts made in preparing the distal end of thefemur to receive the condylar piece 42. If desired, the superior boneengaging surface 46 of the patellar flange piece 41 and the superiorbone engaging surfaces 60, 61, 62 and 63 of the condylar piece 42 may beformed with recesses for receiving bone cement or porous surfaces forbone ingrowth and may also be provided with fixation pins.

[0044] The condylar piece 42 in the embodiment of FIGS. 5-9 is formed asa single unitary piece for implantation. As such, the first condylarportion 50 and the second condylar portion 52 are joined together with aposterior cam 56 which may be formed integral with or welded orotherwise joined to the first and second condylar portions 50, 52. Theengagement end 54 of the condylar piece 42 also has the first and secondcondylar portions 50, 52 joined together by a laterally extending crossmember 57. As will be appreciated by those skilled in the art, the useof the posterior cam 56 will result in sacrificing of the posteriorcruciate ligament. As will be appreciated, in those cases where it maybe necessary to sacrifice the posterior cruciate ligament for otherreasons, the feature of having both a posterior cam 56 and a crossmember 57 for joining the first and second condylar pieces 50, 52 willprovide great rigidity to the condylar piece 42.

[0045] As can be seen in FIGS. 5, 7 and 9, the cross member 57 has asuperior bone engaging surface 57A and a medial surface 57Bapproximately midway between the superior bone engaging surface 57A andthe articulating surfaces 51 and 53 of the first condylar portion 50 andsecond condylar portion 52, respectively. On the posterior side of thecross member 57 is a posterior wall surface 57C extending between thesuperior bone engaging surface 57A and the surface 57B. Opposite theposterior surface 57C is a fourth surface 57D which will engage acorresponding surface to be described of the patellar femoral flangepiece 41.

[0046] The engagement ends 54 for each of the first and second condylarportions 50, 52 each follows a curved path defined by sidewallengagement surface 54A as shown in FIGS. 5 and 6. Each of the curvedengagement wall surfaces 54A extends to the general area defined by theposterior wall surface 57C of cross member 57. (See FIG. 5). Thepositioning of the joint defined by the surfaces 54A of the condylarpiece 42 and the mating surfaces of the patellar femoral flange piece 41is important and should be in the vicinity of the normal femoral tidemark which is a low stress area of contact by sliding engagement of thepatella. By providing the joint in this area, the prosthesis has greatability to function as desired with no separation of the patellarfemoral flange piece 41 from the condylar piece 42 followingimplantation. The normal femoral tide mark corresponds to the area ofthe inferior chamfer cut of a routine total knee arthroplasty.

[0047] The patellar femoral flange piece leading end 48 has a pair ofcurved engagement surfaces 64 following a contour for mating engagementwith the respective surfaces 54A of the condylar piece 42. Centrallypositioned between the curved engagement surfaces 64 is a central wallsurface 65 which, when the patellar femoral flange piece 41 is engagedto the condylar piece 42, lies in substantially the same plane as thesurface 57C of cross member 57. (See FIG. 9). The central wall surface65 extends superiorly from the patellar engaging surface 43 to a ledge66 intended to rest upon the surface 57B of cross member 57. The ledge66 extends away from the central wall surface 65 to a central engagementsurface 67 which is intended to engage the surface 57D of cross member57. A bone engaging surface 68 extends from the central engagementsurface 67 toward the anterior end 45.

[0048] As shown in FIGS. 6, 7 and 9, the condylar piece 42 may besecured to the patellar femoral flange piece 41 by means of screws 68extending through apertures 69 extending through engagement end area 54of the respective first and second condylar portions 50 and 52, throughthe engagement end surfaces 54A and into aligned threaded apertures 71extending inwardly from the curved engagement surfaces 64 of thepatellar femoral flange piece 41.

[0049] Referring to FIG. 8, there is shown the articulating surfacedefined by the patellar engaging surface 43 of the patellar femoralflange piece 41 and the articulating surface 59 of the condylar piece 42in the area of the joint defined by the mating surface 54A of thecondylar piece 42 and surface 64 of the patellar femoral flange piece41. As can be seen in FIG. 8, the respective surfaces 43 and 59 arerecessed slightly at such joint to provide a slight dip 73 so that anymovement of the patellar member P over such joint will leave a slightgap between the surface of the patellar member P and the surfaces 43 and59 at the dip 73.

[0050] The presence of the gap and the dip 73 has a two-fold advantage.It reduces the amount of stress in that area of the joint defined by themating surfaces 54A and 64 at the surfaces 43 and 59. Additionally, ifthere is a slight mismating of the patellar femoral flange piece 41relative to the condylar piece 42 such that one of the surfaces 43 or 59were slightly high or lower than intended for precise fixation, thepresence of the dip 73 will serve to prevent the patellar member P fromcontacting and being subjected to premature wear by a sharp corner ofthe higher piece.

[0051] Referring to FIG. 10, there is shown a further embodiment similarto that of FIGS. 5 through 9 but one in which there is provided acondylar piece 42A having the first condylar portion 50A is joined tothe second condylar portion 52A only by a posterior cam 56A. Under thisembodiment, the patellar femoral flange piece 41A has a central wallsurface 65A centrally positioned between curved engagement surfaces 64A.The central wall surface 65A extends throughout the thickness of thepatellar femoral flange piece 41A. Therefore, there is no ledge similarto the ledge 66 shown in FIG. 5. All other features of the embodiment ofFIG. 10 are similar to corresponding features of the embodiment of FIGS.5, 6, 7, 8 and 9.

[0052] Referring to FIGS. 11, 11A and 11B, there is shown a furtherembodiment of femoral component 40B similar to that of FIGS. 5 through 9but one in which there is provided a condylar piece 42B having the firstcondylar portion 50B joined to the second condylar portion 52B only by across member 57B and a modified connector means for fastening thecondylar piece 42B to the patellar femoral flange piece 41B.

[0053] The cross member 57B is provided with an extension 130 extendingsuperiorly (i.e., downwardly as viewed in FIGS. 11 and 11A) from thecross member 57B. Both the cross member 57B and the extension 130 areprovided with a common dovetail slot 132. The extension 130 is anintegral unitary part of the cross member 57B and, in cross section, hasa generally semicircular cross sectional configuration with the sidefacing the patellar femoral flange piece 41B having a pair of flat faceson opposite sides of the dovetail slot 132.

[0054] The patellar femoral flange piece 41B, has a configurationsimilar to that of the patellar femoral flange piece 41 as shown in FIG.5, including a central wall surface 65B extending from a patellarengaging surface 43B, a ledge 66B and a central engagement surface 67B.A bone engaging surface 68B extends from the central engagement surface67B toward the anterior end 45B. Extending superiorly from the boneengaging surface 68B is an extension 134 having a dovetail 136 sized tobe snugly received in the dovetail slot 132 of the extension 130 withconforming mating surfaces. The dovetail 136 and dovetail slot 132 couldhave other crossectional configurations from that shown in FIGS. 11, 11Aand 11B such as circular or rectangular. As will be appreciated and ascan be seen from FIGS. 11A and 11B, the dovetail 136 is an integralunitary part of the extension 134; however, it extends outwardly fromthe surface 67B and upwardly from the surface 68B to join with surface66B.

[0055] The respective extensions 130 of the condylar piece 42B and 134of the patellar femoral flange piece 41B, when joined together with thedovetail 136 positioned in the dovetail slot 132 will cooperate todefine a substantially cylindrical configuration; however, if desired, adifferent configuration, such as square, rectangular or rounded, couldbe utilized.

[0056] Preparatory to implantation of the condylar member 42B andpatellar femoral flange piece 41B, an aperture is drilled or otherwiseformed in the femur of sufficient size to receive the extensions 130 and134.

[0057] Following positioning of the condylar piece 42B in the preparedfemur with its extension 130 positioned in the prepared bone cavity, thepatellar femoral flange piece 41B is moved therein, the dovetail 136 isaligned with the dovetail slot 132 and the patellar femoral flange piece41B is moved toward the prepared femur with the dovetail 136 slidingthrough the dovetail slot 132 until the surface 66B of the patellarfemoral flange piece 41B contacts the anterior surface of cross member57B. Desirably, bone cement will be positioned in the prepared apertureof the femur to engage the adjoined extensions 130 and 134.

[0058] Referring to FIGS. 12 and 13, there is shown an embodiment of atwo-piece femoral component 74 with a first piece 75 of a patellarflange area having a patella engagement surface 76 and a second piece 77having a medial condyle portion 78 and a lateral condyle portion 79formed as an integral unitary piece. The second piece 77 has a series offlats 96, 97, 98, 99 for engagement with a prepared distal end of afemur.

[0059] The first piece 75 has an abutment wall 81 extending from thepatella engagement surface 76 and positioned to engage a correspondingabutment wall 82 of the second piece 77. The line of juncture betweenthe abutment wall 81 of the first piece 75 and the abutment wall 82 ofthe second piece 77 is in the area of low patella/femoral contact whichis a low stress area of the femur. The abutment wall 81 extends onlypartially through the thickness of the first piece 75. The abutment wall81 joins with a second wall 83 disposed substantially at right anglesthereto (See FIG. 13). The second wall 83 extends to an end wall 84.Extending outwardly from the end wall 84 toward the plane defined by theabutment wall 81 is a ledge 85 having an upper surface 86 with a tongueor dovetail 87 projecting upwardly therefrom. The tongue 87 and uppersurface 86 extend throughout the breadth of the first piece 75. Thetongue 87 is provided with a pair of reverse taper surfaces 88 whichflare outwardly from one another in a direction away from the uppersurface 86.

[0060] Extending outwardly from the abutment wall 82 of the second piece77 is an insert ledge 90 having an upper surface for mating engagementwith the second wall 83 of the first piece 75. The lower portion of theinsert ledge 90 opposite the upper surface has formed therein a dovetailgroove 92 extending the full breadth of the second piece 77 and sized toreceive the tongue 87 of the first piece 75. As can be seen from FIG.13, when the first piece 75 and second piece 77 are joined together,there will remain a gap 93 between the end wall 84 of the first piece 75and the end of the insert ledge 90 of the second piece 77. In order toprevent the engaged first piece 75 and second piece 77 from movinglaterally relative to one another, there is provided a tapered pin 94which may be driven into the gap 93 to function as a wedge putting thetongue 87 into compression in the dovetail groove 92 formed in the lowersurface of the insert ledge 90.

[0061] Referring to FIGS. 14 and 15, there is provided anotherembodiment of prosthesis 100 with a first piece 101 having both apatellar flange area 102 and an integral, unitary lateral condyleportion 103. The prosthesis 100 also has a second piece 104 which is amedial condyle piece. The first piece 101 has a first abutment wall 105extending generally laterally and a second abutment wall 106 extendinggenerally longitudinally with a curved wall section 107 joining thefirst abutment wall 105 and the second abutment wall 106. Protrudingoutwardly from the second abutment wall 106 is a projection 110 havingsidewalls 111 (only one of which is shown) tapering inwardly toward oneanother as they extend outwardly from the second abutment wall 106 andend walls 112 tapering inwardly toward one another as they extendoutwardly from the second abutment wall 106. The tapering sidewalls 111and end walls 112 are joined by an outer wall 113 substantially parallelwith the second abutment wall 106. The projection 110 is integral andunitary with the remainder of the first piece 101 and may be formed by amilling process, for example. A threaded aperture 114 extends throughthe projection 110 from the outer wall 113 and, preferably, extends intothe adjacent portion of the first piece 101.

[0062] The second piece 104 has a first abutment wall 115 positioned toengage the first abutment wall 105 of the first piece 101, a secondabutment wall 116 positioned and sized to engage the second abutmentwall 106 of the first piece 101 and a curved wall 117 for engagementwith the curved wall 107 of the first piece 101. Formed in the secondwall 116 is a recess 118 contoured to snuggly receive the projection 110of the first piece 101. A laterally extending passageway 108 extendsthrough the second piece 104 in alignment with the threaded aperture 114of the first piece 101 when the second piece 104 is engaged thereto.

[0063] In order to join the second piece 104 to the first piece 101there is provided an elongated screw 120 having a threaded section 121for mating with the threads of the threaded aperture 114 of the firstpiece 101. The screw 120 has a cylindrical section 122 of largerdiameter than the threaded section 121 and sized to be snugly receivedin the passageway 108 of the second piece. The screw 120 has an enlargedhead 123 sized to fit in a countersunk area of the passageway 108 at theouter edge of the second piece 104.

[0064] Referring to FIGS. 16 and 17, there is shown a two-piece femoralcomponent 140 including a first piece 141 having both a lateral condyle142 and a medial condyle 143 formed as part of an integral, unitarypiece. The second piece 144 defines a patellar flange area of thefemoral component 140. The second piece 144 has a contoured abutmentwall 145 including a first flat surface 145A extending inwardly from thelateral side, a second flat surface 145B extending inwardly from themedial side of the second piece 144 and a recess defined by first andsecond side walls 145C and a bottom wall 145D. The sidewalls 145C taperinwardly toward one another as they extend from their respective flatsurfaces 145A and 145B to the bottom 145D. Preferably, the bottom wall145D is curved; however, it could be flat.

[0065] The first piece 141 is provided with an abutment wall 146 havinga contour to be snuggly engaged to the abutment wall 145 of the secondpiece 144. As such, the abutment wall 146 includes a tongue 147contoured to fit snuggly in the groove defined by sidewalls 145C andbottom wall 145D of the second piece 144. The tongue 147 is defined bysidewalls 146C, 146C and an end wall 146D contoured to snuggly engagedthe wall 145D forming the bottom of the groove of the second piece 144.The walls 146C, 146C taper inwardly toward one another as they extendtoward the wall 146D and snuggly engage the tapered sidewalls 145C ofthe second piece 144.

[0066] The second piece 144 has formed therein a first passageway 148Awhich extends inwardly from the lateral edge and is substantiallyparallel to the first flat surface 145A and a second passageway 148Bwhich extends inwardly from the medial edge and is substantiallyparallel to the second flat surface 145B. A passageway 149 is formed inthe tongue 147 in a position to be aligned with the passageways 148A and148B when the first piece 141 is engaged to the second piece 144, withthe tongue 147 fitting in the groove. A pin 150 may be inserted throughthe passageway 148B, the passageway 149 and the passageway 148A tosecure the first piece 141 to the second piece 144. The pin 150 could becylindrical and press fit into the respective passageways 148A, 148B and149 assuming the passageways were cylindrical or could be taperedassuming such passageways had the appropriate taper. Additionally, oneof the passageways, passageway 148A, for example, could be threaded, inwhich case the pin 150 would have a threaded end for engagementtherewith.

[0067] In each of the embodiments, the respective lines of juncturebetween abutting walls of the assembled pieces have been selected to belocated generally in the area of the normal femoral tidemark which is alow stress area.

[0068] Referring now to FIG. 18, there is shown a tibial componentgenerally designated by the numeral 161. The tibial component 161includes a tibial base 162 and a tibial stem 163. The tibial base 162has an inferior surface 164 intended to engage the prepared proximal endof the tibia of the patient and a superior surface (not shown) to whichmay be affixed a plastic insert contoured to be engaged by the condylarportions of a femoral component. The plastic insert may have one of anumber of well known mechanisms for being attached to the tibial base162 such as a dove tail locking mechanism, for example. The plasticinsert may be inserted either laterally or proximally depending on thespecific design of the tibial base and the condition of the patient asdetermined by the surgeon. Extending distally from the inferior surface164 is a base extension 165 having a generally cylindrical shape butwith a pair of fixation wings or fins 166 extending outwardly from thecylindrical portion of the base extension 165. A platform 167 is raisedfrom the inferior surface 164 and follows a contour encircling the baseextension 165 including the wings 166. The wings 166 function asfixation fins for maintaining the tibial base 162 in a fixed rotationalposition when implanted on the prepared proximal end of the tibia. Thetibial base 162 is provided with a notch 168 to accommodate theposterior cruciate ligament and a plurality of apertures 169 forreceiving screws for engagement to an augmentation block, if one isneeded, or for securing the tibial base 162 to the proximal end of aprepared tibia.

[0069] The tibial base 162 has a central passageway 170 extending fromthe superior surface 164 and through the cylindrical portion of the baseextension 165. That portion of the central passageway 170 in the baseextension 165 has wall surface which flares outwardly frusto conicallyand defines a Morse taper cavity 295 as it approaches the end of thebase extension 165. A recess defining a notch 240 is formed in the endof the base extension 165. That portion of the passageway adjacent thesuperior surface has a diameter sized to receive a screw 158 and acountersunk area 297 to receive the enlarged head of such screw 158.

[0070] The tibial stem 163 is provided with a pair of wings or fixationfins 171 which, when the tibial stem 163 is engaged to the extension165, will be aligned with and forming extensions of the respective wingsor fins 166 of the tibial base 162. The tibial stem 163 is provided witha Morse taper extension 298 sized to be snugly received in the Morsetaper cavity 295 of the tibial base 162. A shoulder 262 extendsoutwardly from the Morse taper extension 298. A raised tab 242 extendsproximally from the shoulder 202 and is sized to fit snugly in the notch210 and, when so positioned, assures alignment of the fixation fins 171of the tibial stem 163 with the fins 166 of the tibial base 162.

[0071] A threaded passageway 172 is formed in the Morse taper extension298 and is aligned with the central passageway 170 when the tibial stem163 is engaged to the extension 165. The tibial stem 163 is supported onthe tibial base 162 by the screw 158 extending through the centralpassageway 170 of the tibial base 162 and engaged to the threadedpassageway 172. A plug 244 is engaged in the distal end of the tibialstem 163 to prevent blood or other contaminates from entering thethreaded passageway 172. The plug 244 may be secured to the tibial stem163 by means of a threaded extension engaging the threaded passageway172.

[0072]FIG. 18A shows an embodiment similar to FIG. 18 but in which thereis provided a stem extension 250 but not a plug such as the plug 244 ofFIG. 18. The stem extension 250 is provided with a Morse taper 252 atits proximal end 253. A threaded recess 254 extends distally from theproximal end and has a size smaller than the threaded passageway 172. Athreaded screw 258 sized to engage the threaded recess 254 secures thestem extension 250 and the tibial stem 163 to the tibial base 162. Thethreaded screw 258 is small enough to pass through the threadedpassageway 172 without engaging its threads.

[0073] The distal end of the tibial stem 163 has a cavity 260 taperingoutwardly in a distal direction and defining a Morse taper sized tosnuggly receive the Morse taper 252 of the stem extension 250. Twogrooves 270 are formed in the tibial stem 163, on opposite sides,distally spaced from the shoulder 262. The purpose of the grooves 270 isto permit engagement and support for the tibial stem during implantationas will be discussed hereinafter.

[0074] Referring to FIG. 19, there is a shown in section a modifiedembodiment of tibial component 200. Under this embodiment there isprovided a tibial base 202, a tibial stem 204 and a plastic insert 206for engagement with the tibial base 202. The tibial base, as shown inFIG. 19, has a raised wall 208 and a flat superior surface 210. Thetibial base 202 has an inferior surface 212 intended to engage theprepared proximal end of the tibia of the patient. A centrallypositioned short extension 213 extends from the inferior surface 212.

[0075] Extending through the tibial base 202 including the extension 213is a passageway 214. That portion of the passageway 214 adjacent theinferior surface 210 is enlarged from the remainder of the passagewayand is provided with inwardly facing threads 215 in the area adjacentthe inferior surface 210. That portion of the passageway 214 extendingaway from the threads 215 is tapered to define a Morse taper cavity 216throughout the remainder of the thickness of the tibial base 202including the stem 213.

[0076] The tibial stem 204 is provided with an enlarged threaded flange220 sized to engage the threads 215 of the tibial base 202. Extendingfrom the flange 220 is a Morse taper extension 222 sized and contouredto be snuggly received in the Morse taper cavity 216. Extending inwardlyfrom the inferior surface 210 is a cavity defined by a series of flats224 which cooperate to define a hexagon or other conveniently shapedcavity for receipt of a tool for engagement therein for threading thethreaded flange 220 into the threads 215.

[0077] Extending from the cavity defined by the flats 224 is a threadedaperture 225. Extending distally from the Morse taper extension 222 is areduced size cylindrical extension 227.

[0078] The plastic insert 206 has molded therein a metal insert 230having an enlarged flange 232 to ensure its firm engagement to theinsert 206. The insert 206 is provided with a passageway 234 sized toreceive a screw 236 including its enlarged head 238. The metal insert230 is provided with a passageway 240 sized to receive the threadedportion of the screw 236 but smaller than the enlarged head 238.Following engagement of the tibial stem 204 to the tibial base 202, theplastic insert 206 is positioned on the inferior surface 210 within theupwardly extending wall 208. The screw 236 is then engaged to thethreaded aperture 225 to secure the plastic insert 206 thereto.

[0079] In the surgical procedure for implanting the tibial component200, the proximal end of the tibia is prepared by cutting a flat surfaceto receive the inferior surface 212 of the tibial base 202 and a cavityis drilled in the intramedullary canal of the tibia to receive. the stem204. The tibial base 202 is positioned on the prepared flat surface withthe extension 213 positioned in the cavity. The tibial stem 204 is thenpositioned in the passageway 214 with the cylindrical extension 227passing through the Morse taper cavity 216 and into the cavity of theintramedullary canal. Using a tool engaged to the flats 224, the stem isthreadedly engaged to the threads 215 and the base 202 to cause theMorse taper extension 222 to firmly engage the Morse taper cavity 216.As may be seen in FIG. 19, the tibial stem 204 is so contoured relativeto the tibial base 202, that a gap 229 will remain between the distalside of the flange 220 and the surface of the tibial base 202 extendingradially outwardly from the Morse taper cavity 216. This ensures thatthe Morse taper extension 222 will firmly engage the Morse taper cavity216 upon threaded engagement of the threaded flange 220 to the threads215.

[0080] Referring now to FIGS. 20 and 21, there is shown anotherembodiment of tibial component 180 along with a tool 195 for use inimplanting such tibial component in the proximal end of a prepared tibiaT. The tibial component 180 includes a tibial base 181, a tibial stem182 and a plastic insert 179 engaged to the tibial base 181. The tibialbase 181 has an inferior surface 183 intended to engage the preparedproximal end of the tibia T and a superior surface 184 to which may beaffixed a plastic insert 179 contoured to be engaged by a femoralcomponent. The tibial base 181 has raised areas 185 along the anteriorand posterior edges. Each of the raised areas is provided with anundercut wall surface 186 defining grooves for receiving and retainingthe plastic insert 179.

[0081] Extending distally from the inferior surface 183 is an extension187. The tibial base 181 has a central passageway 188 extending from thesuperior surface 184 and through the extension 187. The extension 187and the passageway 188 may be disposed at an angle of up to 100 relativeto a line perpendicular to the superior surface 184 in order toaccommodate the anatomy of the patient.

[0082] The tibial stem 182 is provided with a recess 190 sized andpositioned to become an extension of the passageway 188 of the tibialbase 181. The recess 190 may be threaded for engagement by a threadedscrew 196 extending through the plastic insert 179 and its articularsurface and through the passageway 188 to join the tibial stem 182 tothe tibial base 181. As shown in FIG. 21, the distal end 188A of thepassageway 188 may be tapered to define a Morse taper cavity. The tibialstem 182 is also provided, at its proximal end, with a Morse taperextension 197 sized to snugly engage the Morse taper cavity at thedistal end 188A of the passageway 188. The tibial stem 182 is alsoprovided with a plurality of outwardly facing grooves 189 to assist infixation.

[0083] In preparing the proximal end of the tibia T to receive thetibial component 180, the proximal end T1 of the tibia is cut to formsubstantially a flat surface. A cavity T2 is formed to receive thetibial stem 182. Since the cavity T2 may be oversized, the tibial stem182 is provided with an annular groove 198 sized to receive the tines195A of the tool 195. As can be seen in FIG. 21, with the tines 195Aengaged in the groove 198, the tool 195 can support the tibial stem 182at the proper location relative to the prepared proximal end T1 of thetibia T until such time as the screw 196 is engaged in the threadedrecess 190 to support such tibial stem 182 on the tibial base 181.

[0084] In implanting the tibial stem 163 of the embodiment of FIGS. 18and 18A, a tool similar to the tool 195 may be used to engage thegrooves 270 to support the stem 163 until it is engaged by the screw 158or 258.

[0085] In each of the embodiments of FIGS. 18, 18A, 19, 20 and 21, it ispreferred that the surface of the tibial base which is to be contactedby a plastic insert be polished to a high degree, on the order of four(4) rms or less, to prevent premature wear on the surface of the plasticinsert engaged to the tibial base.

[0086] Description of Surgical Procedure

[0087] A medial parapatellar incision is made from the superior pole ofthe patella to the tibial tuberosity. Medial parapatellar arthrotomy ismade from the inferior edge of the vastus medial is to the tibialtuberosity. A subvastus or mid vastus arthrotomy may be utilized, basedupon patient anatomy or surgeon experience.

[0088] The knee is place in extension and the patella excised withouteversion, using a patellar clamp inserted into the prepatellar bursa, toprevent damage to the anterior skin.

[0089] An extramedullary tibial alignment guide is placed along themedial or lateral half of the tibia and secured with fixation pins. Anextrameduallary alignment guide of the type disclosed in applicationSer. No. 09/973,584 filed Oct. 9, 2001, assigned to the assignee of thepresent invention and incorporated herein by reference, is fixed to thefemur after performing the extramedullary alignment procedure, and thedistal femoral cut is made at the appropriate depth and angle of theimplant, nominally 6° valgus and 10-12 mm depth of cut. As analternative, an intramedullar alignment guide system could be used. Thiscut is taken all the way across both distal femoral condyles, ratherthan being unicondylar in nature. This cut is made at 90° to the femoralshaft.

[0090] The tibial component is implanted first. The fixation surface iscoated with cement, and the modular tibial stem is driven through thereverse Morse taper to lock the tibial stem to the bone.

[0091] The anterior flange component is then implanted, followed by thelateral then medial condyles. Once all pieces are loosely assembledinside the knee and proper alignment is assured, the locking pin isinserted from the side and rigidly fixes the components together. Finalimpaction is then accomplished.

[0092] Lastly, the patella is cemented in place.

[0093] After all cement has hardened and excess is removed, the finalpoly slides in from the side, and is secured with an AP locking clip orscrew, which also helps lock the modular stem in place.

[0094] Routine closure is performed, and rapid rehab program initiated.

[0095] The above detailed description of the present invention is givenfor explanatory purposes. It will be apparent to those skilled in theart that numerous changes and modifications can be made withoutdeparting from the scope of the invention.

We claim:
 1. A femoral component for knee arthroplasty in a knee havinga natural patella or a prosthetic patella comprising (a) a first piecehaving a patellar femoral flange portion including an articulatingsurface for engagement by said patella, said first piece extending froman anterior end toward a posterior end and having one or more engagementsurfaces defining one side of a joint; (b) a second piece defining atleast one condylar portion and having an articulating surface, saidsecond piece extending from said posterior end toward said anterior endand having one or more abutment surfaces cooperating with saidengagement surfaces to define said joint; and (c) a fastener forsecuring said first piece and said second piece together.
 2. The femoralcomponent of claim 1 further including a third piece defining a secondcondylar portion extending from said posterior end toward said anteriorend and having at least one abutment surface cooperating with saidengagement surface to define a second joint and further including asecond fastener for securing said third piece to said first piece. 3.The femoral component of claim 1 wherein said second piece includesfirst and second condylar portions and at least one laterally extendingcross member supporting said first condylar portion to said secondcondylar portion.
 4. The femoral component of claim 3 wherein said crossmember is located adjacent said posterior end.
 5. The femoral componentof claim 3 wherein there is provided a first cross member locatedadjacent said posterior end and a second cross member located adjacentsaid abutment surfaces.
 6. The femoral component of claim 3 wherein saidat least one laterally extending cross member is located adjacent saidabutment surfaces.
 7. The femoral component of claim 6 wherein saidfirst piece includes a central surface extending laterally and first andsecond side engagement surfaces extending from said central surfaceangularly away from each other in a direction toward said anterior end,and wherein said second piece cross member has (i) a medial surfacespaced from said condylar portion articulating surface, (ii) an opposedbone engaging surface, and (iii) a leading surface facing said firstpiece and extending between said medial surface and said bone engagingsurface and wherein said first piece includes a ledge extendinganteriorly from said central surface, said ledge engaged to said crossmember medial surface.
 8. The femoral component of claim 7 furtherincluding a first piece extension extending superiorly from said ledgeand a second piece extension extending superiorly from said crossmember, said first piece extension and said second piece extensionhaving a mating tongue and groove configuration for joining together. 9.The femoral component of claim 3 wherein said first piece includes acentral surface extending laterally and first and second side engagementsurfaces extending from said central surface angularly away from eachother in a direction toward said anterior end.
 10. The femoral componentof claim 1 wherein the articulating surface of said first piece in thearea of said joint and the articulating surface of said second piece inthe area of said joint cooperate to form a recess.
 11. The femoralcomponent of claim 1 wherein said joint is in an area of low stress fromsliding engagement by the patella.
 12. The femoral component of claim 1wherein said second piece has (i) two condylar portions, each having anarticulating surface, and (ii) a connecting section having anarticulating surface extending smoothly from both of said condylarportions articulating surfaces to said one or more abutment surfaces.13. The femoral component of claim 12 wherein said one or moreengagement surfaces and said one or more abutment surfaces each define aseries of intermeshing valleys and projections with apertures extendingthrough or into projections of each of said first piece and said secondpiece and an engagement pin or screw extending into apertures of bothsaid first piece and said second piece.
 14. The femoral component ofclaim 12 wherein one of said one or more abutment surfaces of said firstpiece extends transversely of said first piece and superiorly from itssaid articulating surface throughout only a portion of the thickness ofsaid first piece and further including a wall extending anteriorly fromsaid first piece one abutment surface and a first ledge spaced from saidwall and cooperating therewith to define an insert slot and wherein oneof said one or more abutment surfaces of said second piece extendstransversely of said second piece and superiorly from its saidarticulating surface throughout only a portion of the thickness of saidsecond piece and an insert ledge extending from said second piece oneabutment surface and engaged in said insert slot.
 15. The femoralcomponent of claim 14 wherein one of said first ledge or said insertledge is provided with a slot and the other of said first ledge or saidinsert ledge is provided with a tongue received in said slot.
 16. Thefemoral component of claim 15 wherein said slot and said tongue areprovided with mating reverse tapers.
 17. The femoral component accordingto claim 16 wherein said insert ledge extends only partially into saidslot leaving a transverse space between said insert ledge and said firstpiece and further including an elongated member extending into saidspace.
 18. A femoral knee prosthesis component for use with a tibialcomponent having an articulating surface comprising: (a) a condylarpiece having (i) a superior surface contoured to engage a preparedsurface at the distal end of a femur, (ii) an opposing articulatingsurface contoured for sliding engagement with said tibial componentarticulating surface and extending from (I) a posterior end to (II) anabutment end; (b) a second piece having (i) a superior surface contouredto engage a prepared surface at the distal end of a femur (ii) anopposing articulating surface contoured for sliding engagement by anatural of prosthetic patella and extending from (I) an anterior end(II) an engagement end contoured for mating engagement with saidcondylar piece abutment end; and (c) engagement means for securing saidcondylar piece to said second piece.
 19. The prosthesis of claim 18wherein said condylar piece abutment end and said second pieceengagement end are positioned to be located, following implantation, inan area of low stress from sliding engagement of said patella.
 20. Theprosthesis of claim 18 wherein said second piece comprises (a) acondylar portion and (b) a patellar flange portion.
 21. The prosthesisof claim 18 wherein said engagement means includes (a) apertures in saidcondylar piece and said second piece, and (b) a fastening memberextending into apertures of both said condylar piece and said secondpiece.
 22. The prosthesis of claim 18 wherein said condylar pieceincludes first and second spaced apart condylar portions joined togetherby one or more cross members and said second piece is a patellar flangemember.
 23. The prosthesis of claim 22 wherein said one cross member ispositioned adjacent said posterior end.
 24. The prosthesis of claim 22wherein said one cross member is positioned at said abutment end. 25.The prosthesis of claim 24 wherein said cross member has (i) a superiorbone engaging surface, (ii) a medial surface spaced from said superiorbone engaging surface, and (iii) a second piece engaging surfaceextending between said superior bone engaging surface and said medialsurface.
 26. The prosthesis of claim 25 wherein said second pieceincludes a laterally extending surface positioned between said secondpiece superior surface and said second piece articulating surface, saidlaterally extending. surface being engageable with said cross member.27. The prosthesis of claim 18 wherein said engagement means includes arecess on one of said condylar piece or said second piece and aprojection engageable in said recess on the other of said condylar pieceor said second piece.
 28. The prosthesis of claim 27 further including(i) apertures in said condylar piece and said second piece, at least oneaperture in said projection and (ii) a fastening member extending intoboth an aperture of said condylar piece and an aperture of said secondpiece.
 29. A tibial component for use in knee arthroplasty comprising(a) a tibial base having (i) an inferior surface for engagement with aprepared surface at the proximal end of a tibia and (ii) a passagewayextending through said base; (b) a tibial stem extending distally fromsaid base; and (c) means for engaging said stem to said base.
 30. Thetibial component of claim 29 wherein said passageway in the area of saidtibial stem has a wall surface portion defining a Morse taper and saidtibial stem has a portion defining a Morse taper sized to be snuglyengaged in said passageway Morse taper portion.
 31. The tibial componentof claim 30 wherein a threaded aperture is provided in said tibial stemproximal end portion and further including a screw extending throughsaid tibial base passageway engaged to said threaded aperture.
 32. Thetibial component of claim 30 wherein said passageway Morse taper portiontapers outwardly in a distal direction.
 33. The tibial component ofclaim 32 wherein a threaded aperture is provided in said tibial stemproximal end portion and further including a screw extending throughsaid tibial base passageway engaged to said threaded aperture.
 34. Thetibial component of claim 32 wherein said tibial stem is provided withan outwardly facing annular groove spaced distally from said Morse taperportion.
 35. The tibial component of claim 30 wherein said passagewayMorse taper portion tapers inwardly in a distal direction.
 36. Thetibial component of claim 35 wherein a threaded aperture is provided insaid tibial stem proximal end portion and further including a screwextending through said tibial base passageway engaged to said threadedaperture.
 37. The tibial component of claim 35 wherein said tibial basepassageway is enlarged proximally of said Morse taper portion to definea shoulder extending outwardly from said Morse taper portion and furtherincluding inwardly facing threads proximally of said shoulder.
 38. Thetibial component of claim 37 wherein said tibial stem has a flangeportion proximally of said stem Morse taper portion and outwardly facingthreads engaged to said inwardly facing threads.
 39. The tibialcomponent of claim 38 wherein said flange portion is spaced from saidshoulder when said stem Morse taper portion is snugly engaged to saidbase Morse taper portion.
 40. The tibial component of claim 29 furtherincluding alignment means on said tibial base alignment with alignmentmeans on said tibial stem.
 41. A tibial component for a knee prosthesiscomprising (a) a tibial base having an inferior surface for engagingprepared bone at the proximal end of the tibia, an extension extendingdistally from said inferior surface to a distal end, a passagewayextending through said tibial base, including through said extension,the distal end of said passageway defining a Morse taper; (b) a tibialstem extending from a proximal end to a distal end, said proximal enddefining a Morse taper receivable in said passageway Morse taper. 42.The tibial component according to claim 41 wherein said tibial stem hasa recess extending from said proximal end toward said distal end, saidrecess having threads or other retention means formed therein andfurther including an engagement member extending through said tibialbase passageway and engaged to said threads or other retention means.43. The tibial component of claim 41 wherein said passageway Morse taperportion tapers outwardly in a distal direction.
 44. The tibial componentof claim 43 wherein a threaded aperture is provided in said tibial stemproximal end portion and further including a screw extending throughsaid tibial base passageway engaged to said threaded aperture.
 45. Thetibial component of claim 44 wherein said tibial stem is provided withan outwardly facing annular groove spaced distally from said Morse taperportion.
 46. The tibial component of claim 41 wherein said passagewayMorse taper portion tapers inwardly in a distal direction.
 47. Thetibial component of claim 46 wherein a threaded aperture is provided insaid tibial stem proximal end portion and further including a screwextending through said tibial base passageway engaged to said threadedaperture.
 48. The tibial component of claim 46 wherein said tibial basepassageway is enlarged proximally of said Morse taper portion to definea shoulder extending outwardly from said Morse taper portion and furtherincluding inwardly facing threads proximally of said shoulder.
 49. Thetibial component of claim 48 wherein said tibial stem has a flangeportion proximally of said stem Morse taper portion and outwardly facingthreads engaged to said inwardly facing threads.
 50. The tibialcomponent of claim 49 wherein said flange portion is spaced from saidshoulder when said stem Morse taper portion is snugly engaged to saidbase Morse taper portion.
 51. The tibial component of claim 41 furtherincluding alignment means on said tibial base alignable with alignmentmeans on said tibial stem.
 52. A method of performing knee arthroplastycomprising the steps of (a) providing a multi-piece femoral component,said femoral component including (i) a first piece extending from ananterior end to an engagement surface and having a patellar femoralflange portion including an articulating surface and an opposed superiorbone engaging surface, (ii) a second piece defining at least onecondylar portion extending from a posterior end to an abutment surfaceand having an inferior surface and an opposed superior bone engagingsurface, and (iii) means for securing said first piece and said secondpiece together; (b) preparing the distal end of a femur to receive saidfirst piece and said second piece; (c) positioning one of said firstpiece or said second piece on said prepared femur distal end; (d)thereafter positioning the other of said first piece or said secondpiece on said prepared femur distal end with said engagement surface andsaid abutment surface in contact with one another and cooperating todefine a joint; and (e) securing said first piece and said second piecetogether.
 53. The method of claim 52 wherein step (e) is performedsimultaneously with step (d).
 54. The method of claim 52 wherein step(e) is performed following step (d).
 55. A method of performing kneearthroplasty comprising the steps of (a) providing a multi-piece tibialcomponent, said tibial component including (i) a tibial base having aninferior surface for engagement with a prepared surface at the proximalend of a tibia and a passageway extending through said base, (ii) atibial stem extending distally from said base, and (iii) means forengaging said stem to said base; (b) preparing the proximal end of atibia including forming a cavity along the intramedullary canal of saidtibia; (c) positioning one of said tibial base or said tibial stem onsaid prepared tibia; (d) thereafter positioning the other of said tibialbase or said tibial stem on said prepared tibia; and (e) securing saidtibial base and said tibial stem together.
 56. The method of claim 55wherein said passageway includes a portion in the area of said inferiorsurface which tapers outwardly in a distal direction and said tibialstem includes a tapered extension shaped to snugly engage said taperedportion of said passageway including the steps of positioning saidtibial stem in said prepared cavity and thereafter positioning saidtibial base on said tibial stem with said tibial stem extension in saidtapered position.
 57. The method of claim 56 further including the stepof supporting said tibial stem in said prepared cavity prior topositioning said tibial base thereon.
 58. The method of claim 56 whereinsaid tibial stem has an annular groove distally of said taperedextension and further including the step of engaging said groove with atool to support said tibial stem in said prepared cavity prior topositioning said tibial base thereon.
 59. The method of claim 56 whereinsaid tibial stem tapered extension has a threaded cavity and furtherincluding the step of extending a screw through said passageway andengaging it in said threaded cavity.
 60. The method of claim 55 whereinsaid passageway included a portion which tapers inwardly in a distaldirection and said stem includes a tapered extension shaped to snuglyengage the tapered portion of said passageway and including the steps ofpositioning said tibial base on said prepared tibia proximal end andthereafter positioning said tibial stem through said passageway, intosaid prepared cavity and into engagement with said tibial base.
 61. Themethod of claim 60 wherein said tibial base has inwardly facing threadsand said tibial stem has outwardly facing threads proximally of saidtapered extension and further including the step of engaging saidoutwardly facing threads to said inwardly facing threads.
 62. The methodof claim 61 wherein said tibial component further includes an insertengageable with said base, said insert having a passageway and saidtibial stem extension having a threaded cavity and further extending ascrew through said insert passageway and engaging it in said extensionthreaded cavity.